Overall Objectives. This proposal addresses a Grand Challenge of catalysis: the goal of developing polymetallic, nanocluster "heterogeneous" catalysts that can achieve high %ee catalytic asymmetric synthesis. Novel helical chiral polymers will be synthesized and exploited for their ability to induce, as well as stabilize, chiral-surface nanoclusters for asymmetric catalysis. Those advances will, in turn, fuel the rational development of new asymmetric catalysts of significance to the scientific community and the industries they service. In addition, the studies herein will discover key principles and concepts underlying polymetallic asymmetric catalysts.
The Specific Objectives of this proposal are to investigate three dominant hypotheses: (i) that the nucleation and growth of Pt and Ir nanoclusters, in the presence of specifically designed novel chiral polymers, will allow both superior induction as well as better stabilization of chiral-surface nanoclusters than heretofore possible, due to the match of the >nm length scale of the chiral polymer with the nm length scale of the nanocluster's chiral kink-site surface; (ii) that known polymetallic preferring reactions, such as benzene hydrogenation catalysis, that are also known in Pt and Ir nanoclusters, can be extended to nanocluster asymmetric reduction of prochiral meta-alkylphenols as a prototype test reaction of polymetallic asymmetric catalysis, a reaction of interest to the organic community and the industries that they service; and (iii) that the nature of the chiral catalyst will be nanoclusters with helically chiral, kink-site surfaces of the Whetten type that are, at present, an unrecognized, unstudied and thus completely undeveloped new class of polymetallic asymmetric catalysts.
NSF Team and Its Associated Expertise and Experimental Methods. An NSF Team has been assembled with the required breadth of scientific expertise and physical methods for this Grand Challenge: 3 co-PIs from Colorado State University (CSU), Profs. E. Chen, R. Finke, and T. Rovis, and a collaborator from Pacific Northwest National Laboratories (PNNL), Dr. J. Linehan plus 3 of his colleagues J. Fulton, Dr. W. Shaw, and Dr. S. Kathmann. This NSF Team's combined synergistic expertise spans: nanoscience; materials, inorganic, organic and polymer chemistries; catalysis; asymmetric, nanocluster and chiral-polymer synthesis; kinetics and mechanism; advanced operando characterization methods; and computational chemistry.
The Intellectual Merit of the proposed research consists of at least 3 components: first, the studies outlined will examine and exploit the high probability that growing nanoclusters in the presence of chiral ligands will yield a new class of polymetallic, asymmetric catalysts that are inherently chiral; second, unprecedented aspects of the present NSF proposal include the exploitation of novel, functionalized chiral helical polymers for both superior induction and better stabilization of chiral-surface nanoclusters that can be used to catalyze important asymmetric reactions; and third, the studies outlined will also promise to advance fundamental knowledge of the surface sites of polymetallic, nanocluster catalysts.
The Broader Impacts of the research are at least 4 fold and include its impacts on: (i) discovery and understanding by elucidating the guiding principles and concepts underlying the very timely area of polymetallic asymmetric catalysis; (ii) teaching, training, and learning via an integration of research with education in areas which span much of what is required of a modern chemical scientist when addressing today's broad problems. Moreover, underrepresented, diversity, and undergraduate students will be trained in the superior scientific method which best develops the depth of thought and analysis also required by today's problems, namely the disproof of multiple alternative hypotheses; (iii) networks and partnerships will be developed which will enhance the infrastructure for research and education, notably the partnerships with a National Lab, PNNL, and with the 3 minority serving institutions that CSU partners with, CSU Pueblo, Fort Lewis College, and New Mexico Highlands University; and (iv) the proposed work will also achieve a broad impact on society since the research is in chemical catalysis, an area central to our modern way of life, one with an estimated economic impact of 10 trillion dollars per year worldwide.
" was a collaborative project among three Professors at Colorado State University—a polymer chemist, an organic chemist, and an inorganic/catalytic chemist. The project’s initial goal was to prepare nanocluster catalysts with chiral polymer stabilizers, and that goal was accomplished. Specifically, we have found that: (a) chiral polymer stabilizers can be synthesized by achiral initiators via stereoselective cationic polymerization; (b) the helix sense of chiral polymers can be controlled by chiral side groups; and (c) metal nanoparticles stabilized by such polymer ligands are effective catalysts in the test reactions of alpha-ketoester and meta-cresol hydrogenations. The longer-range, more challenging goal of doing polymetallic asymmetric catalysis with such chiral nanoparticles is still in progress—for example, the preparation of chemical components of modern drugs that have to be asymmetric (or chiral. i.e., as in a left-handed vs a right-handed version) to both have the maximum therapeutic effect and be non-toxic. Initial asymmetric catalysis survey experiments with the chiral-polymer nanoparticles were not successful, but that was not unexpected for this area and challenging research. However and as is often the case in science, the initial survey experiments have led to the next round of ideas and hypotheses for further research. Specifically, the following are the most important leads at present for continued research in this area and in the investigator’s opinions: other chiral polymers that more directly coordinate with the nanoparticles, chiral ionic liquids that can stabilize nanoparticles, and chiral N-heterocyclic carbenes as ligands for the nanoparticles. Three graduate students were also broadly trained with the required thought processes and techniques in how to best approach today's complex, multi-component, multiple-research-group-requiring problems, thereby providing a strong basis for their future careers.
